XLR doesn't mean that it's for microphones only. You can also use XLR for line signals. The preamps are able to handle all gain settings. If you own a TRS to XLR cable somewhere, simply try how the mixer handles the signal. Generally, DI boxes are used to connect keyboards to a mixer. Some keyboards even have XLR connectors built-in, which means that the signals are leveled and balanced inside the keyboard.
The 16R rack mixer might be a better mixer and interface for you. It has 16 "combo locking XLR mic-¼” TRS line" connectors. The 16R is a single core mixer and has only two effect slots. A 24R rack mixer as a dual-core mixer would provide more input channels, more flex mixes and more effects.
